Prior art in the field of metal matrix composites is primarily focused on providing a material for use as a metal substitute to provide a single desired property—light weight. These composites are typically manufactured by adding un-coated particles or through use of open or closed cell foam technology. The emphasis in prior art composite technology is placed on reducing only the weight of the structure, and not in optimizing or modifying the underlying properties of the material so as to impart an application-specific quality.
Consequently, prior art metal composites are light, but do not have the strength, durability or stiffness necessary to compete against materials such as beryllium or aluminum. Closed cell foams are generally very weak, under 5-10 ksi tensile strength, have a poor surface finish, and are not easily machined. Likewise, joining and attaching these composites have inherent technical problems including low quantity processing capability.
Prior art in shielding of metals has been limited to preventing low level electro-magnetic interference by a physical attachment of heavy metal cladding such as nickel, but not in preventing x-ray radiation, prompt nuclear dose, or neutron absorption by use of a micro-engineered composite having the capability inherent to the core composite. In the past, these capabilities have been added through coatings or gluing metal shields onto a previous material.
In addition, prior art utilizing microspheres to form a metal matrix composite involves consolidation using high heat/molten processes and extrusion techniques. High heat causes inter-facial reactions and associated detrimental effects due to oxidation of the molten matrix. Taking the matrix to a molten state creates the possibility of an oxygen reactive liquid phase and allows the matrix to reach a fluid state in which the microspheres can float, melt or segregate within the matrix. High heat/molten processing requires special handling in instances involving molten magnesium and aluminum due to their tendency to react violently in air, thereby also increasing the cost and risk associated with these methods. Other prior art approaches for consolidating composite powders involve forging within a bed of heated, granular particles, typically graphitic in nature. In this process, a less than fully dense article is placed within a heated bed of graphitic powder and pressure is applied without control to the graphite bed via a hydraulic driven ram. During the process, large anisotropic strains are introduced which cause significant particle deformation. During this process, there is no attempt to control the critical pressurization phase of the forging process.
Accordingly, there is a need in the art for a method of producing metal matrix composite materials that: 1) produces light weight composites which consistently and predictably exhibit certain specific desired properties; and 2) a method that avoids both the risk and expense of high-heat molten consolidation processes, and 3) the anisotropic strains that cause significant particle deformation in typical forging techniques. Ideally, such composites would predictably and consistently exhibit application specific qualities (for example for use as radiation hardened materials) and have a lighter mass than nickel, titanium, magnesium, aluminum, graphite epoxy, and beryllium, thereby providing a truly satisfactory substitute for these materials.